/*
object-assign
(c) Sindre Sorhus
@license MIT
*/

'use strict'
/* eslint-disable no-unused-vars */
var getOwnPropertySymbols = Object.getOwnPropertySymbols
var hasOwnProperty = Object.prototype.hasOwnProperty
var propIsEnumerable = Object.prototype.propertyIsEnumerable

function toObject (val) {
  if (val === null || val === undefined) {
    throw new TypeError('Object.assign cannot be called with null or undefined')
  }

  return Object(val)
}

function shouldUseNative () {
  try {
    if (!Object.assign) {
      return false
    }

    // Detect buggy property enumeration order in older V8 versions.

    // https://bugs.chromium.org/p/v8/issues/detail?id=4118
    var test1 = new String('abc') // eslint-disable-line no-new-wrappers
    test1[5] = 'de'
    if (Object.getOwnPropertyNames(test1)[0] === '5') {
      return false
    }

    // https://bugs.chromium.org/p/v8/issues/detail?id=3056
    var test2 = {}
    for (var i = 0; i < 10; i++) {
      test2['_' + String.fromCharCode(i)] = i
    }
    var order2 = Object.getOwnPropertyNames(test2).map(function (n) {
      return test2[n]
    })
    if (order2.join('') !== '0123456789') {
      return false
    }

    // https://bugs.chromium.org/p/v8/issues/detail?id=3056
    var test3 = {}
    'abcdefghijklmnopqrst'.split('').forEach(function (letter) {
      test3[letter] = letter
    })
    if (Object.keys(Object.assign({}, test3)).join('') !==
        'abcdefghijklmnopqrst') {
      return false
    }

    return true
  } catch (err) {
    // We don't expect any of the above to throw, but better to be safe.
    return false
  }
}

export const objectAssign = shouldUseNative() ? Object.assign : function (target, source) {
  var from
  var to = toObject(target)
  var symbols

  for (var s = 1; s < arguments.length; s++) {
    from = Object(arguments[s])

    for (var key in from) {
      if (hasOwnProperty.call(from, key)) {
        to[key] = from[key]
      }
    }

    if (getOwnPropertySymbols) {
      symbols = getOwnPropertySymbols(from)
      for (var i = 0; i < symbols.length; i++) {
        if (propIsEnumerable.call(from, symbols[i])) {
          to[symbols[i]] = from[symbols[i]]
        }
      }
    }
  }

  return to
}
